In wireless communication systems having selectively fading channels, different users experience peaks in their channel quality at different times or at different frequencies. This effect is called multi-user diversity. Multi-user diversity can be exploited in a selectively fading environment by designating users to transmit during times or at frequencies providing favorable channel conditions. For example, in a multi-carrier communication systems, significant performance improvements can be achieved by adaptively allocating to each subscriber multiple subcarriers based on, for example, load traffic information on each subcarrier, signal quality at the subscriber station, whether frequency bands are overused, and level of requests queued at the base station.
Adaptive allocation techniques are generally ineffective in flat fading environments. For example, adaptive allocation may not be practicable in a multi-carrier system with substantially similar subcarrier gains at the subscriber station.